Better batteries to break dependence on fossil fuels

By 2050 world population is projected to reach 10 billion people, and energy needs will double from what we require today. “We are nowhere near ready,” said Héctor D. Abruña at a Charter Day Weekend lecture, “Cornell and the Energy Landscape in the Age of Sustainability” April 26.

Fortunately, the work being done by Abruña and others at Cornell is moving us toward a brighter energy future. The fuel cell and battery technologies they are developing will help power cars, consumer electronics and industry.

The challenges are vast, considering that about 57 percent of the energy currently produced is wasted, said Abruña, the Émile M. Chamot Professor in the Department of Chemistry and Chemical Biology in the College of Arts and Sciences. Current photovoltaic efficiency is around 12 percent for affordable designs; in cars, fuel efficiency is typically about 20 percent. Lighting accounts for 22 percent of all electricity usage in the United States; but the overall efficiency of incandescent bulbs is only 2 percent.

In contrast, fuel cells, which convert chemical energy directly into electricity, can be up to 90 percent efficient.

“If we have any hope of solving the energy problems, we need better energy conversion and storage,” said Abruña, which means better and more affordable designs for fuel cells and batteries.

Fuel cells, explained Abruña, are designed something like a club sandwich, with “bipolar plates” serving the role of bread, with the membrane electrode assembly, containing the catalyst, in between. That catalyst is one of the most expensive parts, often composed of platinum or other precious metals.

Most fuel cells operate in acidic media, which require these costly metals. “One of our main goals at Cornell,” said Abruña, “is to move away from these acidic environments towards alkaline, which require less of these metals.”

Abruña and his colleagues have developed high-throughput methodologies that use fluorescent light to indicate which catalyst compositions have the highest activity. “This technology has accelerated catalyst discovery,” Abruña said.

Better battery design is also necessary, though it’s difficult, since “many batteries operate beyond the thermodynamic limit of some of the materials used,” explained Abruña. “The challenge is to increase energy and power density without compromising safety or the battery’s longevity.”

Abruña is a “big believer” in lithium-sulfur batteries, he said. “I think they have tremendous potential. They’re viable, unlike other popular designs like the lithium-air. Sulfur packs a lot of energy, and it is dirt cheap.” But some of the components of the battery are soluble, thus the capacity fades over time, making the batteries less than optimal.

But Abruña’s lab has found a potential solution. They make nanoscale sulfur spheres and coat them with a layer of polyaniline that keeps the sulfur inside. They remove some of the sulfur so that upon discharge, the assembly can accommodate the resulting volume expansion without breaking, while containing enough sulfur to maintain battery longevity.

Abruña closed his talk with the admonition: “You’re not going to solve the energy problem by separating paper and plastic. We need to transition out of our dependency on fossil fuels and into renewables. As a society, it is really up to us to change.”